1. Technical Field
The present invention relates to a resonator element, a resonator, a resonator device, an oscillator, an electronic device, and a mobile object.
2. Related Art
Resonator elements using a quartz crystal are known. Such resonator elements have excellent frequency-temperature characteristics, and thus are widely used as reference frequency sources, oscillation sources and the like of various electronic devices. Particularly, resonator elements using a quartz crystal substrate which is cut out at a cut angle called an AT cut exhibit frequency-temperature characteristics having a cubic curve, and thus are also widely used in mobile object communication devices such as cellular phones, and the like.
For example, JP-A-2012-114496 discloses that, in an AT cut quartz crystal resonator element having a multistage-type mesa structure, a vibrating portion which is a mesa portion includes a first portion and a second portion having a thickness smaller than that of the first portion, which is integrally formed in the vicinity of the first portion when seen in a plan view, and when the dimension of an AT cut substrate in a direction along a Z′-axis is set to Z, the dimension of the vibrating portion in a direction along the Z′-axis is set to Mz, and the thickness of the first portion of the vibrating portion is set to t, relations of 8≦Z/t≦11 and 0.6≦Mz/Z≦0.8 are satisfied, thereby allowing an equivalent series resistance, or a so-called CI (Crystal Impedance) value to be reduced.
In addition, JP-A-2012-114495 discloses that in an AT cut quartz crystal resonator element having a multistage-type mesa structure in which respective lateral sides of a first portion and a second portion constituting a mesa-shaped vibrating portion which extend in a direction along an X-axis are located within one surface, relations of 8≦Z/t≦11 and 0.6≦Mz/Z≦0.8 are satisfied, thereby allowing the value of an equivalent series resistance to be reduced.
However, in the resonator elements disclosed in JP-A-2012-114496 and JP-A-2012-114495, the equivalent series resistance may be set to 58Ω, for example, when a frequency is 24 MHz, and thus a further reduction in equivalent series resistance is desired.